Intrasession Repeatability and Interocular Symmetry of Foveal Avascular Zone and Retinal Vessel Density in OCT Angiography

Abstract

PurposeTo measure intrasession repeatability and interocular symmetry of the foveal avascular zone area (FAZA) and superficial retinal vessel density (SRVD) using AngioVue Analytics optical coherence tomography angiography (OCTA).MethodsFifty healthy individuals were prospectively enrolled. OCTA scans (3 × 3 and 6 × 6 mm) were acquired twice in right and once in left eyes. FAZA (with and without rescaling) and SRVD for 18 regions (whole, fovea, parafovea, six parafoveal subregions, and nine square zones) were compared between two scans in right eyes (repeatability) and between both eyes (symmetry). Coefficients of repeatability (CRs) and limits of agreement (LAs) were calculated.ResultsAxial length–based image size rescaling had negligible impact on the intrasession CR of FAZA in both 3 × 3- and 6 × 6-mm images. The intrasession CRs for the foveal SRVD were 3.3% and 6.1% in the 3 × 3- and 6 × 6-mm OCTA images, respectively. Age and axial length did not influence test–retest variability of FAZA or SRVD. The interocular LAs in FAZA (0.039–0.059 mm2) was comparable to its CR. However, the interocular LAs in foveal SRVD were −4.5% to +3.8%, with 13% of the cohort showing an interocular difference greater than the CR.ConclusionsFAZA repeatability is not influenced by image size correction, and foveal SRVD is more variable in 6 × 6- than 3 × 3-mm OCTA images. Low image quality may contribute to interocular SRVD asymmetry.Translational RelevanceCRs and LAs can be used to set a threshold for true changes in FAZA and SRVD in longitudinal studies of healthy individuals.

Intrasession and Between-Visit Variability of Retinal Vessel Density Values Measured with OCT Angiography in Diabetic Patients

“…A change of less than 4.53% might simply be due to the measurement inaccuracy of OCTA, which is unable to reliably detect change of less than 4.53%. Our results are in a good harmony with the findings of a previous study on healthy subjects, where a CR of 4.1–4.64% for the whole scan and a CR of 4.4–4.85% for the parafoveal VD in the 3 × 3-mm OCTA images were calculated 23 , 34 .…”

“…Similarly to previous studies on healthy subjects 18 , 34 , we have found that OCT angiography provides excellent intrasession and between-visit reproducibility of measurements in the same subject. In this study we demonstrated in diabetic patients that both intrasession and between-visit repeatability of OCTA measurements are comparable, however, both intrasession and between-visit CV values were higher for the foveal avascular zone area compared to CV values of the macular vessel density.…”

“…In addition, we have provided coefficient of repeatability (CR) values for different OCTA metrics as well, since these data may have direct implications on the follow-up of this population. The coefficient of repeatability can be interpreted as the smallest change in OCTA metrics that represents true change 32 , 34 . This parameter accounts for both random and systematic error in its scores and there is a consensus on the advantage of considering measurement error as calculated by the CR over the Intraclass Correlation Coefficient (ICC) 32 , 33 .…”

Variability of Foveal Avascular Zone Metrics Derived From Optical Coherence Tomography Angiography Images

“… 18 – 20 However, as with all laterally based measurements in retinal images, individual differences in ocular magnification and axial length need to be corrected in order to accurately compare area measurements between subjects or across studies. 1 , 21 The need to measure axial length, as well as the large variation of area seen in normal individuals, 1 – 3 , 19 , 22 – 25 makes it difficult to use area as a measure to compare small changes associated with disease progression between subjects or for identifying an FAZ as “abnormal.” While these limitations are less important when assessing repeatability of OCTA during a single visit, 26 they represent important barriers to comparing data across different studies and populations.…”

Assessing the Influence of OCT-A Device and Scan Size on Retinal Vascular Metrics

“…33 Similarly, Rabiolo et al showed that FAZ area was interchangeable across 3 × 3 mm, 6 × 6 mm, and 12 × 12 mm scan sizes using the AngioPlex, but that vessel density was highly dependent on scan size. 34 In contrast, Chen et al reported a ∼ 10% difference in FAZ area between 3 × 3 mm and 6 × 6 mm scan sizes (0.234 mm 2 and 0.259 mm 2 , respectively) 35 but nonsignificant vessel density differences when using the AngioVue. 35 In studies comparing scan size, the issue of image magnification is less critical, as we are only interested in relative differences between scan dimensions from the same device.…”